Verdigris

[fm tim]

I want to create the greenish color called Verdigris on brass. 

The dictionary says that it is created by the action of acetic acid on copper, but I am working with brass.

The one source of acetic acid I have identified is vinegar.   Does anyone have experience with vinegar on brass, or do I need a stronger agent or another agent?

[ottawa]

I know if you let brass set in vinegar to long it gets  black . the best way is to try it a a test piece to see how it works.

[elk killer]

over night in amonia works well
put amonia in bottom of coffee can, set the brass on some wood so only the fumes get to it...
not in the amonia..

[T*O*F]

There are two methods to achieve the color you want on brass.  Both are recipes used by professional craftsmen for eons.

#1
3 oz Potassium bitartrate (cream of tartar)
1 oz Ammonium chloride
7.5 oz Copper nitrate
3 oz Sodium chloride (non-iodized table salt)
13 oz boiling water

Dissolve the salts in the boiling water and apply the hot solution to the brass with a swab or piece of sponge.  When the desired effect has been attained, wash and dry.  This is the fast method.

#2
3 oz Copper carbonate
1 oz Ammonium chloride
1 oz Copper acetate
1 oz Potassium bitartrate
8 oz Strong vinegar

Dissolve the salts in the vinegar and paint the object daily with the solution for 3-4 days.  This is the slow method.

[Lucky R A]

  You could take the easy safe way. and purchase a bottle of Jax "green patina"

[Smoketown]

fm tim,

How much verdigris do you want?
How much time do you have?

Well oiled veg or chrome tanned leather will do it just as it does to cartridge brass.
Think bullet loops ...

Cheers,
Smoketown

[fm tim]

A great start.  Thanks to all.

[JCKelly]

Eric A. says ammonia makes brass brittle.

I would say the problem is that ammonia cracks brass.

This is something that industry relearns every half-century or so. The first to record, if not be harmed by, this were the Brits. Whilst bringing the Light of Victorian Civilization to the Indian subcontinent with .577 Sniders, they noticed that the brass cartridge cases all cracked during monsoon season. Called it "season cracking" Of course, during this rainy time they stored their ammo in the horse barn. On and on and on, mice do quite a job on brass items in storage, too.

Some people do use ammonia to get patina on brass, which is OK unless you leave the thing in too long. Then it cracks. No, I do not know what is "too long", surely over the weekend is. Also may depend on whether it is a casting or some sheet which has been formed a lot, like thimbles.

your P.I.T.A. metallurgist

[bob in the woods]

If you use a cleaning patch from swabbing a gun barrel, or lock pan [ black powder ] to wipe down your brass, you will have your desired finish in short order.

[rich pierce]

Verdigris, or the green, slimy patina, is a whole different animal from a quick BP residue patina.

[bob in the woods]

Hi Rich.  Yes, I agree, but it is a start. If I leave my 45-100 Sharps brass uncleaned after firing, the mouth of the case and 1/2 in of the wall  will be covered in green verdigris in a few days.  If you use Pyrodex it will happen faster .  Ask me how I know this 

[fm tim]

Again, thanks to all.

I have used most of the "black" strategies on prior builds, but I need the green color over a wide area so a solution like the Jax product seems the best strategy at this point.